It is well known in the art to provide plant containers in which the side walls and base have holes or apertures which permit air to circulate around the container. This feature facilitates air pruning of the roots as the root structure expands by virtue of the plant growing in the container.
Such a plant growth container and air pruning feature is that disclosed in U.S. Pat. No. 5,099,607 to Lawton Pa. This patent discloses a container in which plants are to be grown and comprises of a flexible rectangular section of material moulded into a lattice of recesses and corresponding protuberances. The section is formed into a cylinder with the vertical edges of the section overlapping so that opposite recesses and protuberances form a nesting arrangement which is then fastened together to produce the container. Roots are guided into the recesses which converge to holes providing the air interface for air pruning to take place. This plant growth container has the advantages of being easily adaptable in diameter and is reusable.
A similar plant growth container is also disclosed in U.S. Pat. No. 4,939,865 to Whitcomb et al. This patent describes a container comprising a set of upwardly extending removably joined side panels having a lattice of protuberances and corresponding recesses converging to holes. The panels are generally rectangular, bendable and have vertical edge joints so that one or more of the side panels can be joined together to form a generally cylindrical open-topped container. Like the container of U.S. Pat. No. 5,099,607 this container has the advantages of being easily adaptable in diameter and is reusable.
These open topped containers have a number of common disadvantages. As the joints of these containers are on the vertical, it is difficult for a user to peel back a section of the section or panel to inspect the root ball of a plant within.
A further disadvantage is in the strength of the container. These containers are generally constructed of a lightweight material which has the flexibility to bend into the cylindrical form easily. As such, this compromises the weight of the contents i.e. soil and trees or plants, which can safely be transported. Further, when used with a base, the base has a tendency to collapse inwards under the weight of the plant which is placed in the container. The problem is exacerbated for large diameter containers due to the relatively small surface area of support given to the base and the fact that the base rests on a downwardly slopping surface within the container. Thus a great number of bases must be manufactured to provide for each possible diameter size due to the fact that the diameter of the base must be a close match to the diameter of the container.
A yet further disadvantage of this open topped container is that current formers used to make the sections are flat topped formers. These produce a flat surface that deflects the roots back as opposed to guiding them gently towards the air interface.